01998naa a2200181 a 450000100080000000500110000800800410001910000200006024501330008026000090021352014160022265300330163865300200167170000200169170000240171170000190173577300620175421319542021-05-21 2021 bl uuuu u00u1 u #d1 aMATOS, G. F. de aEvolution and function of nitrogen fixation gene clusters in sugarcane associated Bradyrhizobium strains.h[electronic resource] c2021 aBradyrhizobium spp. are well known to mediate biological nitrogen xation (BNF) as microsymbionts inhabiting nodules on leguminous plants. However, they may also contribute to plant growth via freeliving N2 xation (FLNF) in association with nonlegumes. Notably, several Bradyrhizobium strains from sugarcane roots display FLNF ctivity. Among them, Bradyrhizobium sacchari is a legume symbiotic species, whereas strains AG48 and M12 are non-symbiotic. In the present study, a phylogenomic pproach was applied to study peculiarities of these and other Bradyrhizobium strains with respect to N xation (nif) gene content in order to reveal genetic features that enable FNLF in Bradyrhizobium spp. All FLNF strains carry an ancestral ?non-symbiotic? nifgene cluster (NSC). B. sacchari also contains a second ?symbiotic? nif-gene cluster (SC), a characteristic observed in only three of 156 evaluated genomes. B. sacchari stood out and presented a high level of sequence divergence between individual nif-gene homologues and we discuss scenarios for the evolutionary origin of these clusters. The transcript level of NSC nifH gene increased during FLNF, when compared to symbiotic conditions. The data suggest that sugarcane roots harbor diverse Bradyrhizobium spp. that are genetically adapted to a dynamic environment where leguminous and non-leguminous host plants are alternately available. aBiological nitrogen fixation aFabaceae family1 aROUWS, L. F. M.1 aARAUJO, J. L. S. de1 aBALDANI, J. I. tEnvironmental Microbiology, Published Online 15 May 2021.